Add CAGRA InnerProduct test and fix a bug

[enp1s0]

There is no CAGRA InnerProduct test in cuVS while there was in RAFT. This PR adds the test.

Also, this PR

• fixes an error that occurs when building a CAGRA graph with NN Descent + InnerProduct (cpp/src/neighbors/nn_descent_*.cu)
  • Could not pass the idx.metric() == params.metric validation in the nn_descent::detail::build function.
• updates RAFT_EXPECT in the nn_descent::detail::build function for better error understanding
• fixes the NN Descent API sample codes

[cjnolet]

Thanks for this fix @enp1s0!

[cjnolet]

/merge